Trump’s claim might seem like an exaggeration, played up for drama, but research suggests that once people board the Trump train, there’s little that can prod them to jump off. (You could probably say something similar about Hillary Clinton supporters.) As much as we like to think that we use reason to evaluate evidence and come to conclusions, “It really goes back assward, a lot of times,” said Peter Ditto, a psychologist at University of California, Irvine. “People already have a firm opinion, and that shapes the way they process information.” We hold beliefs about how the world works and tend to force new information to fit within these pre-existing narratives. Psychologists call this motivated reasoning, and it means that once people have thrown their support behind Trump or Clinton, they will tend to downplay or ignore things that paint their candidate in a bad light.

In a study conducted in October,1 researchers presented 507 self-identified Republicans and 986 self-identified Democrats with actual things that Trump had said — some of which were true and some of which were false. The researchers might explain, for instance, that “Trump said that the MMR vaccine causes autism,” or they would simply present the assertion that “The MMR vaccine causes autism.” Then they asked people, “How much do you believe this statement?”

“If we told participants that it was Trump that said the misinformation, Republicans were much more likely to believe it and Democrats were much less likely to believe it,” said Briony Swire2, a Ph.D. candidate in cognitive psychology at the University of Western Australia, who conducted the study with colleagues at MIT and the University of Bristol. On a 10-point scale, Republicans rated the misinformation 4.8 and Democrats 3.2 when it was attributed to Trump. A similar partisan split appeared with the true statements — Republicans were more likely than Democrats to believe factual statements when told that Trump had said them. “People relate to the world with their partisan lens,” Swire said.

Fact-checking Trump didn’t change his supporters minds about him in Swire’s study. After presenting participants with the various statements, the researchers debriefed the volunteers on which of these statements were true and which were false. Even when Trump supporters accepted that some of Trump’s statements were untrue (recognizing that a vaccine doesn’t cause autism, for instance) they did not change their voting preference. In other words, Trump supporters were willing to acknowledge that some of Trump’s statements were lies, but this didn’t alter their enthusiasm for him. “I guess it means that politicians like Trump can spread misinformation without losing support,” Swire said.

If you think Trump will bring jobs back to the U.S. and he tells you that his “constant badgering at packed events” has convinced Ford to cancel plans to move a facility to Mexico, learning that Ford has made no such change of plans may just remind you that Trump is talking about creating jobs in the U.S. Instead of receiving the information as a reason to doubt Trump’s truthfulness, you view the correction as evidence that he’s serious about the jobs issue, and so the fact-check reinforces your pre-existing belief that Trump will put American jobs first. And if the correction comes from a news source that you perceive as biased against your candidate, you may simply dismiss it out of hand anyway.

Similarly, if you’re a Clinton supporter who thinks that Republicans are on a crusade to tear her down, then a recent FBI investigation concluding that her use of a private email server had been “extremely careless” but not worthy of criminal charges will probably only reinforce your belief that your candidate is being subjected to a witch hunt.

The current election is taking place in an atmosphere of mistrust, and “mistrust is the Swiss Army knife of motivated reasoning,” Ditto said. People have very intense feelings about Trump and Clinton — largely negative feelings. “These are the two most dislikable candidates ever to run — so the temperature is turned up,” Ditto said. “People on the left say that Trump is a moral abomination and he lies all the time, and you can take these things and imagine someone on the right saying the same thing about Clinton,” Ditto said.

People whose support for Trump arises from animosity toward Clinton or discontent with the status quo are unlikely to be swayed by facts or revelations about Trump’s truthfulness or policy, and the same goes for Clinton supporters who loathe Trump. To understand why someone might acknowledge that Trump has made outrageous comments and yet still support him, consider what an internet commenter calling himself Bryan wrote. He’s supporting Trump “because a vote for Trump is as close to a punch in the face to the ENTIRE establishment as you can get.” And then there’s this: “Is he a racist misogynistic asshole? Yes. Is he a big-time buffoon who makes a joke of himself? Yes. Is he a narcissistic snob who makes careless controversial statements? Yes,” wrote a Trump supporter at Quora. “But, he will have the independence to implement any legislation without having any external pressure. And that is good for the country.” Someone who has already acknowledged that Trump is a “racist misogynistic asshole” won’t be swayed to drop support for the candidate based on new examples of his being any of those things.

To riff on a line from another presidential candidate named Clinton, it’s not the facts stupid, it’s the story you weave around them. I live in western Colorado, where the local economy has been devastated by the closing of numerous coal mines. To the people in my area with “end the war on coal” yard signs and bumper stickers that say, “Coal keeps the lights on,” Donald Trump’s promise that “If I win we’re going to bring those miners back,” holds obvious appeal. Even more so when the alternative is Clinton’s far less appealing (but factually more correct) message — those coal jobs probably aren’t coming back so we need to develop new industries for regions that depend on mining. When the choice is an appealing fib versus an ugly truth, it’s human nature to prefer the answer we wish were true.

CORRECTION (July 20, 9:45 a.m.): An earlier version of this article misstated the government agency that investigated Hillary Clinton’s email server. It was the FBI, not the CIA.

VIDEO: Donald Trump’s upcoming challenges

Footnotes

The study has been submitted to a journal but is not yet published.

Swire is Australian, so she doesn’t have a vote in the election.

By comparison, PolitiFact has checked 223 statements by Hillary Clinton and found that 51 percent of them were “true” or “mostly true” (only 10 percent of Trump’s statements received these ratings). Thirteen percent of Clinton’s statements were deemed false or “pants on fire” false.

Christie Aschwanden is FiveThirtyEight’s lead writer for science. @cragcrest